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Abstract

Bottlenose (Tursiops sp.) and common dolphins (Delphinus sp.) are amongst the most common small cetaceans. They both have a world-wide distribution from warm temperate to tropical waters inhabiting pelagic and coastal waters, and they both show high morphological variability throughout their range, leaving the taxonomic issues in both species unresolved. This thesis provides a comparative assessment of these two species, by molecular analysis, especially in the context of comparing coastal and pelagic populations of each species. The aim is to better understand the evolutionary processes and the factors involved in shaping the population structure in small delphinids. The strategy 1 followed was: 1) Analyse the population structure of the bottlenose and common dolphins on a worldwide scale and compare large scale patterns in the context of known similarities and differences with respect to life history. 2) Analyse populations on a smaller geographic scale (Mediterranean Sea and South Africa) to further understand the relationship between habitat and population generic structure. On a worldwide scale, bottlenose dolphins showed high genetic diversity and strong population structure, both between different and similar morphotypes, suggesting limited gene flow. Two populations, of the same morphotype, have diverged considerably to the extent that they should be considered different species. Common dolphins showed lower genetic diversity and weak population structure even over a large geographic range, suggesting higher level of gene flow. However, this species also has similar morphotypes that were genetically differentiated from one another. On a smaller geographic scale, we found a similar pattern of population structure, with the bottlenose dolphin showing higher population divergence than common dolphins. However, both species provided evidence supporting the role of habitat in defining population structure in these species. These findings should facilitate the development of effective conservation and management strategies for these species, especially for the specific case studies for populations in the Mediterranean Sea and off the Natal coast of South Africa.